1. Field of the Invention
The invention relates to a navigation system, and more particularly, to an apparatus and method for controlling display luminosity according to an operational mode in a navigation system.
2. Background of the Related Art
Generally, a navigation system indicates a computed current position of a moving subject on a map displayed on a screen using information received from a global positioning system (hereinafter, “GPS”). The navigation system provides a user with various kinds of information, for example, information necessary for traveling in a particular direction for a moving subject, a distance to a destination, a current traveling speed of the moving subject, a path set up by a user prior to traveling, and an optimal path to the destination.
Navigation systems are currently loaded on various moving subjects, such as ships, planes, and vehicles, to be globally used in confirming a current position or location and a traveling speed of the moving subject and/or deciding a traveling path. Specifically, the navigation system receives radio waves indicating, for example, longitude, latitude, and altitude from a plurality of satellites belonging to GPS, computes a current location of a moving subject, and then informs a driver of map information, including, for example, the current location visually and/or audibly. The navigation system is also provided with supplementary functions, such as a dimming function for adjusting screen luminosity of a display to fit peripheral illumination in order not to attract the attention of a driver who is driving.
FIG. 1 is a block diagram of a related art auto dimming device in a car A/V system disclosed in Korean Patent Application No. 10-1998-0034368. Referring to FIG. 1, the related art auto dimming device in a car A/V system includes a detector 110 that detects peripheral luminosity, an A/D converter 120 that divides a voltage of a detected analog voltage value into prescribed grades to convert it to a digital value, a microcomputer 130 that outputs an output from the A/D converter 120 as a potential meter grade value in prescribed grades, a potential meter 140 that outputs an analog voltage value in prescribed grades from an output of the microcomputer 130, and a TFT LCD 150 that displays a level varying according to the voltage value from the potential meter 140.
The detector 110 includes a photoconductive cell cds1 that detects the peripheral luminosity, a switch SW1 that switches on/off illumination power ILL power, load resistors R1 and R2 connected to the switch SW1, and a transistor Q1 connected between the load resistors R1 and R2. The photoconductive cell cds1 outputs a voltage difference according to a variation of resistance due to a peripheral light change.
An operation of the above-described device will be explained with reference to FIG. 1 as follows.
First, once power is applied to an illumination terminal, such as a car tail lamp power on/off switch of the illumination power ILLpower, an auto dimming function signal is released. Namely, if the power is applied from the illumination terminal, the switch SW1 is turned on so that a voltage is applied to the transistor Q1 via the resistors R1 and R2. Since a collector potential of the transistor Q1 stays at a low level, a potential difference of the photoconductive cell cds1 of the detector 110 is grounded to be 0V. Hence, the auto dimming function is forcibly released to perform prescribed illumination only. Yet, as a voltage value is transferred from the photoconductive cell cds1 in an off-mode of the switch SW1, the auto dimming function is established.
A variation level of the voltage value of the photoconductive cell cds1 ranges 0V to 5V, whereby a voltage level is output differently according to external luminosity, the presence of sunlight, a fluorescent lamp, or a glow lamp. Hence, it is able to provide an output voltage variable according to external luminosity.
Once the photoconductive cell cds1 detects external luminosity, the detected analog voltage is input to the A/D converter 120 so that the analog value can be converted to the digital value to be input to the microcomputer 130. The A/D converter 120 divides the variation level into seventeen grades. Namely, the luminosity of the LCD display 150 is divided into various grades for illumination.
Subsequently, the microcomputer 130 outputs data to the potential meter 140 provided at its rear end according to the seventeen grades of the A/D converter 120 to fit a resistance grade of the potential meter 140. The output data corresponding to the grade value of the potential meter 140 from the microcomputer 130 is then input to the potential meter 140 to be output as a DC analog voltage value corresponding to the data value. And, an output of the potential meter 140 is output to the TFT LCD display 150 to implement auto dimming of the car A/V system to correspond to the peripheral luminosity.
The related art auto dimming device, which discerns daytime luminosity, nighttime luminosity, and external luminosity from each other, relatively raises the illumination of the LCD display 150 and backlight thereof due to the influence of the external light in daytime, thereby enhancing a user's visibility. However, as the navigation system needs various functions to comply with the tendency toward digital convergence, the related art auto dimming device fails in controlling the LCD luminosity adaptively.
Thus, the related art navigation system fails to be provided with the appropriate LCD dimming function but indiscriminately controls the illumination of the LCD so that there exists no difference in luminosity between a video mode, such as a TV mode and an audio-only mode, thereby wasting power consumption and interfering with the attention of a user who is driving due to the LCD image.